One of the most commonly performed invasive procedures in modern medicine is the insertion of an intravenous (“IV”) or arterial catheter. Unfortunately, such procedures can require substantial skill for success, and even experienced and skilled practitioners have significant failure rates. This results in considerable pain and anxiety for the patient who may have to endure multiple attempts. Patients will often vividly recall having suffered failed IV or arterial insertions in the past.
Many failures can be attributed to a single point in this multi-step procedure: the attempt to thread the catheter after the vessel has been punctured by the needle and flashback of blood has occurred. Beginners often fail to appreciate that when flashback occurs, the needle tip (and orifice) are in the vein or artery, but the catheter tip may have not yet entered the vessel. They attempt to thread the catheter immediately upon flashback and thereby “blow” the insertion, because the catheter tip pushes the pliant vessel off the needle. Experienced practitioners, on the other hand, realize that following flashback, the entire needle/catheter assembly must be inserted an additional 2 mm or so before catheter threading is attempted. Yet the practitioner must be cautious to avoid over-insertion. Over-insertion will cause the sharp tip of the beveled needle to penetrate the “back” distal wall of the vessel, thereby resulting in failure and a painful hematoma. Accordingly, IV needle insertion is a precise, and often difficult, procedure for practitioners to perform.
By way of further illustration of this undesirable outcome, reference is made to FIG. 1, which depicts a typical needle and catheter arrangement 100 according to the prior art. The arrangement 100 includes a hollow metallic (typically surgical stainless steel) insertion needle 110 with a lumen 112 of appropriate size/diameter for the blood vessel 120 into which it is inserted (For example, needle sizes 14 gauge (G), 16 G, 18 G, 20 G, 22 G or 24 G). The distal end of the needle includes a conventional sharp, beveled, chisel-like tip 114 with an open orifice 116 that extends proximally into the lumen directly from the angled cylindrical orifice edge. This tip includes a distal point 118 that is quite sharp and enables piercing of the skin layer 122 and vascular wall 124 as shown with minimal discomfort for the patient. Overlying the needle 110, proximal of the tip 114 is a closely conforming catheter 130 constructed from a biocompatible polymer of conventional design. The distal end 132 of the catheter ends proximally of the angled tip 114, forming a small-diameter step that normally passes into the puncture hole created by the tip 114. The proximal end of the arrangement 110 typically includes an assembly with a distal portion that defines a fitting 142 interconnected with the catheter 130 and a proximal portion 144 that is interconnected with the needle. The two portions 142 and 144 can be withdrawn axially from each other so as to withdraw the needle 110 proximally from within the catheter lumen, while maintaining or advancing the catheter 130 distally with respect to the vessel 120 so as to thread and implant the catheter fully into the vessel.
As shown in FIG. 1, the needle tip 114 has been inserted by the clinician into the vessel 120 and the now-open path between a distal-most portion 150 of the tip orifice 116 and the bloodstream causes the flashback of blood through the needle lumen 112, which is visible in a flash chamber 160 at the proximal end. However no portion (or substantially no portion) of the catheter's distal end 132 has entered the vessel 120. Thus, an inexperienced or inattentive clinician may attempt to thread the catheter immediately upon such flashback. This premature threading generally causes the clinician to blow the insertion, because the catheter tip 132 pushes the pliant vessel 120 away from, and off of, the needle as the catheter is driven distally in an attempt to implant it in the vessel.
As set forth above, more experienced practitioners are aware that, following flashback, the entire needle/catheter arrangement 100 should be inserted an additional distance before catheter threading is attempted. Unfortunately, as further illustrated in FIG. 2, the sharp, beveled point 118 on the distal tip of the needle 110 may penetrate the distal back wall 210 of the vessel 120 during this additional insertion. This may result in a failed insertion and a painful hematoma.